1. Field of the Invention
The present invention relates to a decoding of a receiving sequence coded by the turbo codes and, more particularly, a turbo decoding device for executing the decoding by means of a soft-input/soft-output decoding.
2. Description of the Related Art
In recent years, the turbo coding system gets into the spotlight as the channel coding system that takes a step closer to the Shannon limit. In the mobile phone which deals with the multimedia and the importance of which is increasing in the data communication, such turbo coding system is employed as the coding system that gives a lower bit error rate.
Various proposals of its implementation in the mobile device, and so on as well as its theoretical study have been made since the turbo codes was proposed. For example, in Patent Literature 1 (JP-A-2001-285079), in order to achieve a miniaturization and a lower power consumption of the LSI used to decode the turbo codes, a decoding of the convolutional codes and a decoding of the turbo codes, which are executed before now by a dedicated decoder respectively, are managed by one LSI.
FIG. 10 is a block diagram showing a configuration of a turbo decoding device in the prior art. In FIG. 10, a reference numeral 1001 is a first soft-output decoder, 1002 is a second soft-output decoder, 1003 is a first interleaver, 1004 is a second interleaver, 1005 is a deinterleaver, and a 1006 is a hard decision unit.
Also, 1007 to 1009 are received turbo codes, 1007 is transmission information, 1008 is a first coded signal derived by coding the transmission information, and 1009 is a second coded signal derived by interleaving and coding the transmission information.
The first interleaver 1003 interleaves the transmission information 1007, the second interleaver 1004 interleaves a reliability information likelihood that the first soft-output decoder 1001 outputs, and the deinterleaver 1005 deinterleaves a reliability information likelihood that the second soft-output decoder 1002 outputs.
Also, the transmission information 1007, the first coded signal 1008, and an output of the deinterleaver 1005 are input into the first soft-output decoder 1001. Also, an output of the first interleaver 1003, an output of the second interleaver 1004, and the second coded signal 1009 are input into the second soft-output decoder 1002.
In the turbo decoding device constructed in this manner, the first soft-output decoder 1001 and the second soft-output decoder 1002 repeat a decoding process alternately and then the hard decision unit 1006 hard-decides an output of the second soft-output decoder 1002, so that the decoding of the turbo codes is carried out (for example, see Non-Patent Literature 1: K. Yamaguchi, H. Imai, “New coding system getting near to Shannon limit: Turbo Codes”, NIKKEI ELECTRONICS, No. 721, pp.163-177, Jul. 13, 1998).
The turbo decoding device in the prior art executed a decoding process by operating two soft-output decoders alternately. Therefore, assume that a processing time that one soft-output decoder needs to calculate totally a likelihood calculation of a length N is M, a processing time of at least 2× M or more is consumed as a time required for the decoding process of transmission information of a length N.